[libcxx-commits] [libcxx] [libc++] `std::ranges::advance`: avoid unneeded bounds checks when advancing iterator (PR #84126)

[Jan Kokemüller via libcxx-commits]

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@@ -188,11 +229,12 @@ constexpr bool test() {
         check_forward_sized_sentinel<int*>(                        range, range+size, n, expected);
       }
 
-      {
-        // Note that we can only test ranges::advance with a negative n for iterators that
-        // are sized sentinels for themselves, because ranges::advance is UB otherwise.
-        // In particular, that excludes bidirectional_iterators since those are not sized sentinels.
+      // Exclude the `n == 0` case for the backwards checks.
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jiixyj wrote:

I guess it isn't strictly needed. I thought it would be more appropriate for the `check_backward` tests to only test the `n < 0` case as the `n == 0` case is covered by the `check_forward` tests above. I added a comment to that effect.

https://github.com/llvm/llvm-project/pull/84126